1. Field of the Invention
The present invention relates to a system for converting a still picture into television signals.
2. Description of the Prior Art
A slide, photographic print or like information bearing medium with a still picture recorded thereon may be processed to pick up a television (TV) signal thereoutof by, for example, the optical scanning system which is disclosed in U.S. Pat. No. 4,306,252. In this prior art system, a scanning mirror is mechanically caused into a reciprocal pivotal movement to vertically scan a still picture, while a one-dimensional solid-state image pickup device (linear image sensor) scans it horizontally by means of electronics, thereby scanning an entire still picture in a raster fashion. To output a video signal in a TV signal format, the mirror is angularly displaced by mechanical means at a playback rate of video signals. Concerning one-frame two-field interlace scanning as in the NTSC standard television system, the mirror is caused to swing at the rate of 60 fields per second for vertical scans. While driving the mirror in a reciprocal movement at the scanning speed, the system switches the optical path and reverses the scanning direction upon every vertical scan so as to prevent fast returns of the mirror during blanking periods. For so switching the optical path, however, the system has to rely on intricate optical and mechanical arrangements including a disc which has reflecting and transmitting portions and rotates in unison with the scanning mirror.
Also known in the art is a method in which a mechanical scanning arrangement is used to scan a still picture to form a video signal at a rate slower than an expected rate of the video signal on reproduction of the image. This method, to output a video signal as a TV signal, once stores the video signal formed by the slow scans in a storage which is installed in a video signal processing apparatus and, then, reads it out at the reproduction rate. Such a method cannot be practiced unless the video signal is processed in the form of digital signals. Another drawback is that the use of such a storage is undesirable from the economical standpoint in view of the numerous bits in one frame of image data and the frequent demand for storing numerous frames.